FFAG as a phase rotator for the PRISM project A. Sato, M. Aoki, Y. - - PowerPoint PPT Presentation
FFAG as a phase rotator for the PRISM project A. Sato, M. Aoki, Y. Arimoto, Y. Kuno, M. Yoshida, Osaka University S. Machida, Y. Mori, C. Ohmori, T. Yokoi, K. Yoshimura, KEK Y. Iwashita, Kyoto ICR S. Ninomiya, RCNP Physics motivation
Yoshida, Osaka University
Yokoi, K. Yoshimura, KEK
1 0
1 0
1 0
1 0
1 0
1 0
1 0
Upper limits of Branching Ratio Y e a r
KL
0 → µeK
+ → πµeµA→eA µ → eee µ→ eγ
History of LFV Search limits
Search for the Lepton Flavor Violating Process
Future experiment will cover most
One of the important particle physics topics achievable with PRISM is a search for lepton-flavor violating muon rare processes. Lepton flavor violation attracts much attention, theoretically and experimentally, since it would have a large discovery potential to new physics beyond the Standard Model, for instance supersymmetric extension to the Standard Model. An example of proposed experiments of such at PRISM is a search for μ−−e− conversion process in a muonic atom at a sensitivity of 10^-18.
Sensitivities are superb in muon systems
muon decay in orbit
nucleus
µ−
µ
− → e −ννµ
− + (A, Z) → νµ + (A,Z −1)nuclear muon capture
µ − + (A, Z) → e− + (A,Z)
neutrinoless muon nuclear capture (= m-e conversion) physics beyond the Standard Model A negative muon stopped in some material :
High Intensity
The potential sensitivity achievable in searches for rare processes is ultimately limited by the number of muons available. The muon beam intensity of 1011−1012 μ−/sec should be required, yielding about more than 1020μ− per year.
High Purity
Beam contaminations are necessary to be removed, to reduce any background associated with them. It is already shown that the past experiments like SINDRUM-II have already seen a background event just above the signal region, and they suspect that it comes from pion contamination in a beam through radiative pion capture. Therefore, it is the most important to reduce pion contamination in a beam.
Narrow Energy Width
Narrow energy spread of the beam will allow a thin muon stopping target to improve the momentum resolution of e− detection, which is limited by energy loss in the muon stopping target.
High Resolution Spectrometer
To improve the intrinsic momentum resolution in an e− spectrometer, it is critical to construct a thin tracking chamber system.
PRISM is a project to provide a dedicated source of a high intensity muon beam with narrow energy- spread and small beam
“Phase Rotated Intense Slow Muon source”. The aimed beam intensity is 10^11−10^12μ±/sec, four orders
available at present. It is achieved by a large solid-angle pion capture with a high solenoid magnetic field. Narrow energy spread can be achieved by phase rotation, which accelerates slow muons and decelerates fast muons by a radio frequency (RF) field. The pion contamination in a muon beam can be removed by a long flight path in PRISM so that most of pions decay
muon intensity 10^11-10^12μ/sec kinetic energy 20MeV energy spread +-(0.5-1.0)MeV beam repetition 100-1000Hz pion contamination < 10^-18
Anticipated PRISM beam design characteristics
Pion capture section
The highest beam intensity in the world could be achieved by large-solid angle capture of pions at their production.
Decay section
π − μ decay section consisting of a 10-m long superconducting solenoid magnet.
Phase rotator
to make the beam energy spread narrower. To achieve phase rotation, a fixed-field alternating gradient synchrotron (FFAG) is considered to be used.
FFAG advantages:
synchrotron oscillation
need to do phase rotation
large momentum acceptance
necessary to accept large momentum distribution at the beginning to do phase rotation
large transverse acceptance
muon beam is broad in space
Phase rotation is a method to achieve a beam of narrow energy spread. The principle
and decelerate fast muons by a strong radio- frequency (RF) electric field, in order to yield narrow longitudinal momentum spread. By phase rotation, the initial time spread is converted into the final energy spread. It corresponds to 90 degree rotation of the distribution of the muons in the beam in the energy-time phase space.
1 2 3 4 5 1 2 3 4 5
RF : 5MHz, 128kV/m
ΔE/E = 20MeV+12%-10%
RF : 5MHz, 250kV/m
ΔE/E = 20MeV+4%-5%
Initial Phase After 1 turn After 2turns 54.4 61.2 68.0 74.8 81.6MeV/c After 3turns After 4 turns After 5turns
54.4 61.2 68.0 74.8 81.6MeV/c Initial Phase After 1 turn After 2 turns After 3 turns After 4 turns After 5 turns
In order to achieve a high intensity muon beam, it is necessary for the PRISM-FFAG to have both of large transverse acceptance and large momentum acceptance. Furthermore, long straight sections to install RF cavities are required to obtain a high surviving ratio of the muon. Therefore, the PRISM-FFAG requires its magnets to have large aperture and small opening angle. In such magnets, not only nonlinear effects but also fringing magnetic field are important to study the beam dynamics of FFAGs. Three-dimensional tracking is adopted to study the dynamics of FFAG from the beginning of the lattice design procedure. In this process, quasi-realistic 3D magnetic field maps, which are calculated applying spline interpolation to POISSON 2D field, were used instead of TOSCA field in order to estimate the optical property quickly
r1 r2 r3 r4 r5 r x(θ)
N=8 k=5 F/D = 7.1 r0=5m
N=10 F/D=8 k=5 r0=6.5m
140000πmm mrad 3000πmm mrad 35000πmm mrad
Table 2: Present parameters of PRISM-FFAG
10 Magnet type Radial sector DFD triplet C-shaped Field index (k-value) 4.6 F/D ratio 8.0 Opening angle F/2 : 2.2deg. D : 2.2deg. Half gap 17cm Maximum field
Average radius 6.5m for 68MeV/c Tune horizontal : 2.69 vertical : 1.30
5m
RF PS RF AMP RF Cavity FFAG-Magnet Kicker Magnet for Extraction Kicker Magnet for Injection
scaling radial sector Conventional type. Have larger circumference
ratio.
triplet (DFD) F/D ratio can be tuneable. the field crump
has mirror symmetry at the center of a straight section.
large aperture important for achieve a high intensity muon
beam.
thin Magnets have small opening angle. so FFAG
has long straight section install RF cavities as mach as possible
C-shaped intermediate pole made of anisotropic magnet material. the
magnet can have not only constant gap but also smaller fringing field. A scaling condition can be easy to fulfill. the intermediate pole filters out local irregularity of the magnetic field distribution. Thus the accuracy of the pole shape is not necessary and the number
trim coils k value is tuneable. Therefore, not only
vertical tune and also horizontal tune are tuneable.
500 1000 1500 2000 2500 3000 3500 4000 2 4 6 8 10 12 14 16 18
(Deg.) Bz (Gauss)
r=580 cm r=600 cm r=620 cm r=640 cm r=660 cm r=680 cm r=700 cm r=720 cm z = 0 cm
1 2 3 4 5 6 7 8 9 10 580 600 620 640 660 680 700 720
r (cm) F/D ratio
1 2 3 4 5 6 7 8 9 10 580 600 620 640 660 680 700 720
F Componet D Componet
r (cm) k value + 1
The 3D magnetic field was calculated by using a 3D field calculation code, TOSCA. These figure shows results of the calculation
value (middle) and the F/D ration (bottom) as a function of radius. The local k and F/D ratio were calculated by the BL integration and they are almost constant over the beam
fulfilled.
50 Gauss 100 Gauss
Proton Synchrotron RF System 50 100 150 200 250 2 4 6 8 10 12 Frequency (MHz) Field Gradient (kV/m) SATUNE MIMAS CERN PSB CERN PS AGS ISIS KEK BSTR KEK PS J-PARC 50GeV MR
50GeV MR Upgrade KEK-HGC PRISM
Ferrite Cavities J-PARC MA Cavities (High Duty) PRISM Cavity Since the muon is an unstable particle (life time~2.2us), it is crucial to complete phase rotation as quickly as possible in order to increase a number of surviving muons. In present design, PRISM requires very high field gradient of 200kV/m at the low frequency (4-5 MHz). As compared with usual cavities, PRISM has to operate its cavities at a remarkably outstanding condition.
± Number of gap per cavity 5 Length of cavity 1.75 m Number of core per gap 6 Core material Magnetic Alloy Core shape Racetrack Core size 1.4m × 1.0m × 3.5cm Shunt impedance ∼159Ω/core @ 5MHz RF frequency 4∼5MHz Field gradient 200kV/m Flux density in core 320 Gauss Tetrode 4CW150,000E Duty <0.1% Table 3: Parameters of PRISM-FFAG RF system.
“ ” “ ”
1.00E+09 1.00E+10 1.00E+11 1 10 100 1000 10000 Brf[Gauss] up'Qf SY2 N5C 4M2-302 FT-small FT-large
Magnetic Alloys Ferrites
Characteristics of MA
Thin Tape , 18 mm High Field Gradient
Voltage limit: Brf <Bsat. (1T) and Voltage per layer < 5 V
High Curie Temperature Large core, Rectangular Shape Large permeability (about 2000 at 5MHz) Original Q value is small(0.6). High Q is possible by cut core configuration Thickness -35mm (50mm in future)
PRISM RF core Outer size : 1.4m x 1.0m x 0.35m Inner size : 0.74m x 34 m
Anode PS Clover cavity cavity cavity cavity Heater SG AMP condenser AMP condenser AMP condenser AMP condenser drive AMP
An RF amp system has been constructed. Its performance test is in the works.
Among the all PRISM components, the phase rotator section can be constructed from japanese fiscal year (JFY) of 2003 for five years. FY2003 Lattice design, Magnet design RF R&D FY2004 RFx1gap construction & test Magnetx1 construction & field meas. FY2005 RF tuning Magnetx9 construction FFAG-ring construction FY2006 Commissioning Phase rotation FY2007 Muon acceleration (Ionization cooling)
5m
RF PS RF AMP RF Cavity FFAG-Magnet Kicker Magnet for Injection